REFERENCE ELECTRODE

Abstract: A reference electrode for electrochemical measurements made in aqueous solutions under high pressures and at high temperatures. The reference electrode comprises a metallic conductor wire (1), on the surface of said conductor wire, an insulating layer (2) of its own oxide, on the surface of the wire, an area (3) free of insulating layer, and a metal/salt coating (4) covering the area, serving as an electrochemical element determining the potential.

Description: REFERENCE ELECTRODE The present invention concerns a reference electrode as defined in the preamble to Claim 1. Reference electrodes are used, for instance, in various electro-chemical measurements in aqueous solutions. The circumstances of measurement are often inconvenient owing to high temperatures and high pres¬ sures. A reference electrode for use in such conditions traditionally consists of a silver wire and an insula¬ tor thereupon, the latter usually being of some appro¬ priate plastic material. However, problems are caused in connection with an electrode of this kind by the temperature resistance of the insulator and by the sealing of the electrode when it is being carried through into the pressurized space, because the elastic insulating layer surrounding the silver wire is sub¬ jected to comparatively high pressure when the sealing is made. Owing to the problems just reviewed, accom¬ plishment of electro-chemical measurements in aqueous solutions has been cumbersome at temperatures upwards of 300°C, although temperatures in various applications may vary up to the critical point of water, which is about 370°C. The object of the invention is to eliminate the drawbacks mentioned. The object of the invention is specifically to disclose a novel reference electrode which is simple and easy to manufacture and of which the sealing against a pressurized space is easy to implement. Regarding the features characterizing the invention, reference is made to the Claims section. The reference electrode of the invention for use in electro-chemical measurements made in aqueous solutions under high pressures and at high temperatures comprises a metallic conductor wire, on the surface of the conductor wire an insulating layer of its own ox¬ ide, " an area on the surface of the wire free of insu¬ lating layer and a metal salt coating covering said area and which serves as an electro-chemical element determining the potential. It is thus essential in the reference elec¬ trode of the invention that in it such a metallic con¬ ductor material is used which forms on its surface, or on the surface of which can be formed, a chemically stable oxidized layer serving as electrical insulator. Advantageously, the reference electrode of the invention comprises a metallic zirconium wire upon which, or on the surface of which, a zirconium oxide layer has been oxidized. Zirconium oxide Zr0 2 is a good insulator and thereby forms an adequate insulator on the surface of the zirconium wire between the sur¬ rounding aqueous solution and the wire. In addition there is in the reference electrode on the surface of the wire an area free of the zirconium oxide layer, and this free area has been covered or coated with a mix¬ ture of silver Ag and silver chloride AgCl, which serves in the electrode as an electro-chemical element determining the potential. Other electro-chemical reference couples con- stituted by a solid metal salt and an electrolyte may equally be used in addition to the silver/silver chlo¬ ride (Ag/AgCl) reference couple, such as e.g. a mer¬ cury/mercury chloride (Hg/Hg 2 Cl 2 ) couple. When making a reference electrode according to the invention, it is advantageous first to oxidize the entire surface of the conductor wire to carry a corre¬ sponding oxide layer, whereafter an aperture is made in the oxide layer, i.e., oxide is removed therefrom on a given area so that the metallic conductor wire is ex- posed. The metallic conductor wire is then coated, or covered, e.g. with a mixture of silver and silver chlo¬ ride. This covering is advantageously accomplished by dipping the area to be covered in molten silver chlo¬ ride containing silver in the form of small particles. Advantageously, the area to be covered is a cylindrical area of the wire's mantle, extending around the conductor wire. The mixture covering the oxide aperture is advantageously prepared in that the silver chloride is heated to about 400°C, at which temperature it melts, and silver is added to this in the form of small, fine particles, whereafter the conductor wire, at least its part containing the oxide aperture, is dipped in this molten mixture. The reference electrode of the invention en¬ ables electro-chemical measurements at any temperature and pressure up to the critical point of water, and its sealing to a pressurized shell is easy because it has no separate, yielding insulating layer, instead of which it has an oxide layer on the outer surface of the metallic conductor wire, which renders good sealing possible. In the following the invention is described with the aid of the attached drawing, wherein schemat¬ ically has been depicted a reference electrode accord¬ ing to the invention, or more accurately, the tip de- sign of the reference electrode. The reference electrode depicted in the draw¬ ing comprises a conductor wire 1, consisting of metal¬ lic zirconium. Around this is provided a mantle 2 of zirconium oxide Zr0 2 encircling it substantially on all sides, which has, for instance, been grown by oxidation around the wire to form a continuous insulator shell. The zirconium oxide mantle serving as insu¬ lator has been removed from around the zirconium wire on a certain annular area 3, which extends as a cylin- drical shell over the whole circumference of the zir¬ conium wire at a distance from the end of the wire. Thereafter, the end df the zirconium wire, including the area free of zirconium oxide, has in its entirety and to a certain distance onward from the free area been covered with a mixture 4 of silver and silver chloride in such manner that the metallic zirconium 1 is not in direct connection, or contact, with the space outside the reference electrode. In this way the Ag/AgCl coating will serve as an electro-chemical ele¬ ment determining the potential of the reference elec¬ trode. In the foregoing the invention has been de¬ scribed in detail with the aid of the drawing, while different embodiments of the invention are feasible within the scope of the inventive idea delimited by the claims.

Claims: CLAIMS 1. A reference electrode for electro-chemical measurements made in aqueous solutions under high pres- sures and at high temperatures, characterized in that the reference electrode comprises - a metallic conductor wire (1), - on the surface of said conductor wire, an insulating layer (2) of its own oxide, - on the surface of the wire, an area (3) free of in¬ sulating layer, and - a metal/salt coating (4) covering the area (3), serving as an electro-chemical element determining the potential. 2. Reference electrode according to claim 1, characterized in that the conductor wire is a zirconium wire Zr (1) and on the surface of the wire as insulator is provided a zirconium oxide layer Zr0 2 (2), e.g. grown by oxidation. 3. Reference electrode according to claim 1, characterized in that the metal/salt coating consists of Ag/AgCl mixture. 4. Reference electrode according to claim 3, characterized in that the area (3) has been coated by dipping it in molten AgCl which contains silver in the form of small particles. 5. Reference electrode according to claim 1, characterized in that the area (3) extends on the con¬ ductor wire over its entire circumference. 6. Reference electrode according to any one of claims 1-5, characterized in that the reference electrode is used at all and any temperatures and pres¬ sures up to the critical point of water about 370°C. 7. Reference electrode according to any one of claims 1-6, characterized in that the free area (3) is produced by removing the oxide layer from the area. 8. Reference electrode according to any one of claims 3-7, characterized in that the Ag/AgCl mix¬ ture is heated to about 400°C, whereupon the area (3) is dipped in it.

Inventors: AALTONEN PERTTI, MAEKELAE KARI, SELIN LAURI, AALTONEN, PERTTI, MAEKELAE, KARI, SELIN, LAURI
Applicants: AALTONEN PERTTI, MAEKELAE KARI, SELIN LAURI, VALTION TEKNILLINEN, AALTONEN, PERTTI, MAEKELAE, KARI, SELIN, LAURI, VALTION TEKNILLINEN TUTKIMUSKESKUS
Application year: 1994
Main classification: G01N27
IPC codes: G01N27